Here are some ways to understand the meaning:
* It suggests that there is much more to learn or understand than what has been explored so far. Like skimming the top layer of something without digging deeper.
* It implies that a deeper understanding is still possible and desirable.
* It can be used in a positive or negative sense. For example, it can be used to acknowledge that more work is needed or to express frustration that something has not been fully explored.
Here are some examples of how the idiom can be used:
* "We've only scratched the surface of what this new technology can do." (This implies that there's a lot more potential that hasn't been explored yet.)
* "I feel like I've only scratched the surface of understanding this complex topic." (This acknowledges that the speaker still has much to learn.)
* "The investigation has only scratched the surface of the corruption in the company." (This suggests that there is much more corruption yet to be uncovered.)
In summary, "scratched the surface" is a useful idiom for emphasizing that something has not been fully explored or understood.